German patent document DE 10 2005 012 673 A1, for example, discusses an apparatus for activating at least one driver's cab actuator element, the control system described therein for adjusting the level of the driver's cab in relation to the vehicle frame serving to adjust the level when the vehicle is stationary or to compensate for various load states of the driver's cab or to compensate for roll and/or pitch whilst in motion. The level control system is intended to keep the driver's cab at a horizontal and constant level under all circumstances, whether stationary or in motion.
German patent document DE 26 32 444 A1 likewise discusses a driver's cab height control system, in which the driver's cab is pivotally supported about a horizontal axis in relation to the vehicle frame and is additionally supported on the vehicle frame by two pneumatic actuator elements. A height adjustment valve serves to keep the angular position of the driver's cab constant, the air pressure in the actuator elements being increased in the event of an increased load due to passengers getting in, for example, so as to prevent the rear end of the driver's cab subsiding. By contrast the air pressure in the actuator element is reduced when the load in the driver's cab falls, in order to prevent the rear of the driver's cab rising. Here too, therefore, the position of the driver's cab is adjusted to a horizontal level.
The actuator elements or support elements generally comprise pneumatic springs, which flexibly support the driver's cab relative to the vehicle frame, and generally hydraulic dampers, in order to generate damping forces between the driver's cab and the vehicle frame, which is necessary in view of the unwanted pitch and roll movements of the driver's cab caused by the flexibility of the driver's cab mounting.